1. Field
This disclosure relates to telephony equipment, more particularly to methods and devices providing three-dimensional audio streams.
2. Background
Some telephone equipment may include ‘three-dimensional’ audio capabilities. Multiple audio streams are manipulated to locate each stream in a manner that will cause the user to interpret the streams as being spatially separated. For example, in a four-person conference call, the receiving equipment may manipulate the streams of the three speakers heard at the fourth person's end to ‘place’ one speaker to the listener's left, one to the right and one in the center. This type of manipulation typically allows the listener a better chance at comprehending the multiple streams and alleviates listener fatigue.
Generally, the three-dimensional (3D) audio stream consists of a stereo audio stream in which the left and right tracks are compositions of the original component streams transposed by psychoacoustically manipulating head-related transfer functions (HRTF). The HRTFs attempt to model a 3D environment such as a room and mainly attempt to reproduce reflections that would be heard in such an environment. HRTFs are commonly used and developed for consumer products in the home entertainment market, such as ‘surround sound’ systems for home theaters and stereos.
The use of this type of audio manipulation also occurs in telephonic or other non-entertainment areas. For example, U.S. Pat. No. 5,485,514, issued Jan. 16, 1996, addresses spatially separating a telephone audio stream into right and left streams for headphones, rather than for a one-speaker telephone handset commonly used. U.S. Pat. No. 5,682,196, issued Oct. 28, 1997, presents a system in which personalized audio feedback is provided to a viewer in an interactive television system. U.S. Pat. No. 6,011,851, issued Jan. 4, 2000, discloses an audio processing system in which various audio streams are spatially located at different points relative to the user, allowing the user to spatially separate the audio signals as they are comprehended.
However, a problem with current three-dimensional audio processing has been discovered. It generally occurs in systems where headphones are used, as opposed to point audio sources that are spatially located in front of the user such as those in the system discussed in the '851 patent. In about one-quarter of all users of three-dimensional audio systems, the front-back signal information used to spatially place audio streams is comprehended as in reverse. In these users, audio streams that are manipulated to place that audio stream to the front of the user are actually interpreted as coming from behind the user. Humans typically become uncomfortable and may even become alarmed by sounds coming from behind them. For 3D telephony applications, this is undesirable, as it increases listener fatigue and offsets the efficiency and advantages otherwise gained from conference calls and other multiple audio stream applications.